Thats the partial vin of the chassis it came out of. 1968 Dearborn with the next 6 digits matching the vin.

Casting and date codes are above the starter on passenger side of block.

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Here's a pic I took 15 years ago of my '67 289 for location, C5 = '65. As HoustonGlock stated, you probably have to remove the starter to see them and be prepared with degreaser, a toothbrush and rag to be able to read them. Passengers (right) side rear corner of engine, shelf above oil pan. I don't know when they stopped doing this, in the 90's (E9xxx series)?
See here for decoding casting #'s. Decoding Ford casting part numbers

 

thanks, i was trying to veriry an engine that came out of an 68 mustang. seller said it had 90 thousand miles on it and was pulled from an gt. the two pics provided that it is an 302 but the front of the heads haD A CASTING like a crossover pipe was bolted to it on both heads. never seen anything like that.was looking for a j code block cheap in standard bore. asking price was way to much for the condition . thanks, rich b

 

Well, the partial VIN shows it IS from a Dearborn car and with it less than 500,000 it's a Mustang and not a Cougar. On the OTHER hand, there is no such thing as a "J-Code" block... the 302 casting was used for both "C-Code" 289's and "J-Code" 302's. The defining difference would be in the crank and rods installed. As far as the "casting" you are talking about, could you possibly mean the Thermactor tubes?